Invader GRIM
by nico420
Summary: Using Grim's scythe, Billy accidentally opens a portal to an alternate universe, where he becomes an alien hunter; Gaz makes a friend; Mandy wants to help Zim take over the world with Grim's help; Dib must save the world by stealing Grim's scythe.
1. Chapter 1

**I do not own Invader ZIM, The Grim Adventures of Billy & Mandy, or any of the following characters.**

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**This starts out pretty slowly and takes a while to get into things. Also, it may take me a while to update this.**

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"Grim. Get me a soda," Mandy ordered, without looking up from her book.

"Get it, yourself," Grim said, sticking his nose in the air (or he would be, if he had a nose). Mandy looked up at this, giving him a dangerous glare. "Oh, alright," he sighed, getting up from the couch. "I can't believe I let a little girl _boss_ me around like that," he complained to himself in the kitchen, feeling a loss of self-esteem. "I'm the _Grim Reaper,_ for death's sake." He grabbed a soda from the fridge and shuffled back into the living room, where Mandy was reading her book and Billy was watching TV. Mandy accepted the drink without saying thank you; not that Grim expected her to.

"I'm bored!" Billy said, turning his attention from the TV. He looked at Grim, as if for answers.

"What do you want _me_ to do about it?" Grim said.

"Let me play with your scythe!"

"Ha! I don't think so..."

"But—"

"_No,_ Billy. And if I ever catch you with me scythe—" Grim held up the aforementioned weapon—"you won't live to regret it, mon."

Billy only giggled at him.

Grim sighed. Sometimes he couldn't tell if the boy even understood a word he was saying.

It had been about ten years, give or take, since Grim lost that bet with the children and was forced into being their "best friend forever." They had grown a lot, since then; they weren't really children, anymore. Mandy had already graduated from high school, and Billy, who'd failed a grade, was just finishing up his senior year.

Mandy still styled her short blonde hair into devil horns and she tended to wear a lot of pink; as it had always been her favorite color. Billy dressed very casually and could never be seen without a hat. Personality wise, they remained very much the same. Mandy was still cynical, contemptuous, and controlling—not to mention, downright scary, sometimes—and Billy hadn't gotten much smarter, either.

What surprised Grim was that Billy and Mandy were still friends.

He wasn't completely sure why they were such good friends in the first place—he figured it was because Billy was the only person who wasn't afraid of Mandy, but would still do whatever she wanted, simply, because he had no qualms about doing it—but he _was_ sure that she would ditch him, eventually; on account of the fact that he wasn't the brightest tool in the shed, and she was a fairly intelligent girl who might find friends more suited to her; but she seemed to really care about the boy. _Either that, or she scares everyone else away,_ Grim laughed to himself.

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Mandy left just before it got dark, and Grim stayed at Billy's because it was his turn to keep him (he still went back and forth between their houses, every few days).

It was chilly out, but she didn't live too far away. When she got home, her parents were sitting on the couch, watching television; looking tense as she walked through the door.

"H-How was your day, sweetie?" Her mother stammered.

Her parents were always nervous around her—she was _that _intimidating. When she was a bratty child, she could be very scary if she didn't get her way, and it was easy to boss them around. Her parents even hired a nanny to straighten her out when she was little, but Mandy was just too much for her. She'd always had the uncanny ability to control those around her, as though she was God and this was her world; which was the way she saw it most of the time. Once in a while, though, life would bite her in the ass and remind her that some things were out of her control.

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Speaking of control...

"Don't you get it, Gaz?! He's trying to take over the world!" Dib said, trying to convince his sister to help him with one of his plans.

_Err. _Gaz growled under her breath. "Leave me alone, Dib. Can't you see, I'm playing a video game," she said, without looking up from her hand-held device.

"You're always playing video games... This is _real life,_ Gaz! If we don't do something, the earth will be doomed! _DOOMED!_"

_That's it._ Dib was getting on her last nerve.

"Go... AWAY... _Dib._ Before I—"

"Okay, okay," her brother said, cutting her off before she could unfurl a list of death threats against him. He pouted, and left to go spy on Zim or something; leaving her alone for once.

_Ahhh... Peace and quiet._

It wasn't that she wouldn't have helped him if the earth was actually in trouble, but Zim was too stupid to cause any real damage. She didn't know why her brother had to run around, yelling about him, all the time. It was so _annoying. _That alien was all he ever talked about, for _years. _Having been here this long should have been a clear indication that he would probably never succeed in destroying the world; at the very least, Dib didn't need to worry about it every second of his life.

Indeed, not much had changed...

Dib—now, twenty—was taller and ganglier, with the same scythed black hair, only it was longer; and he still wore thick, circular glasses and a signature black trench coat. He was still interested in the paranormal and obsessed with catching Zim.

He still annoyed the hell out of his sister.

Gaz hadn't changed much, at all... She had chin-length purple hair that curled up in the front—giving the impression of jaws—with bangs that came down like fangs, on her forehead. Her wardrobe consisted of mostly purple and black, and she still wore her favorite skull necklace, every day. She was cold, distant, and anti-social—never able to muster up enough interest in any one person. People, as a whole, generally, annoyed her. Even more so, now that she was a senior in high school, and the students she had grown alongside were as stupid as ever; with their pointless dramas and superficial lives.

She had taken a step back to examine the world around her, and found that humanity just did not make sense. Cynical and nihilistic, she could not understand the frivolous ways of her species. _For being the smartest creatures on Earth, humans are complete idiots, _she thought. _Apparently, Irkens are no better._


	2. Chapter 2

The next day was Saturday, which meant no school. Mandy was spending the day and night at Billy's, so she woke up around eleven and left for Billy's around noon. When she got there, he and Grim were in the kitchen, making sandwiches.

"Make me one, too." She sat down at the table. Grim got out two extra slices of bread. "So, what's on the itinerary?"

The guys looked at each other and shrugged, then looked back at Mandy.

"I don't know," Grim said.

"What's an it_in_erary?"

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_School..._

_It certainly doesn't make anybody smarter, _Gaz thought, looking around.

It was hard, being smarter than most people. It was hard to listen to them; to watch the way they interacted with each other; to have conversations with them. It was hard to believe people could _be_ that stupid. It was hard to not laugh at them; to not feel sorry for them; to not hate them.

If she were a different kind of person, she might have been lonely. She didn't have any friends, and—although, she loved her brother—she couldn't stand listening to his voice for too long. Not to mention, their father—a famous scientist—was always busy, and barely had any time to spend with them.

That was probably the only thing that bothered her.

It didn't seem to bother Dib.

She preferred to be alone, but... She wouldn't mind having a friend.

When she was little, she used to gaze at the stars with her older brother. He'd tell her to watch out for UFOs. He said he wanted to know that there was more out there than this. All he had to do was spot one. Just one.

He'd also said that he wished he could meet an alien; that he wanted them to take him away from here. Away, to outer space.

That always stuck with her. She thought about it, especially, now. Now, that she felt stuck in a world she didn't belong to. Now, that she wanted, desperately, to get away from here. For someone to whisk her away to a place where she actually fit in. Now, that there was proof of there being more out there, and that it's inhabitants were just as stupid, if not stupider than that of Earth's.

The only worlds that suited her were in her game consoles.

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That night, as soon as Grim and Mandy were fast asleep, Billy crawled out of bed to play with the scythe.

He tip-toed to it, quietly; giggling. He loved messing with Grim's things. Not only, because they were supernatural and interesting, but because he loved doing anything he wasn't supposed to.

However—in doing so—he accidentally opened a portal, which sucked him and his sleeping friends into an alternate universe.

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"Uhh... Grim..." Mandy said, surveying their new whereabouts.

Just a moment ago, she had been sound asleep at Billy's. Now, she was standing in a large, open field—_in her nightgown_—alongside him and Grim; watching a boy fight an alien over some sort of remote control. Off to the side, there was a hyperactive robot and a girl with purple hair. The girl was watching with disinterest.

Mandy noted that the sky was purple, too.

She wondered if this was a dream.


End file.
